1. Field of the Invention
This invention relates principally to basic oxygen furnaces (BOF) and chemically pitch bonded refractory brick; as noted herein, however, there may be exceptions and the invention is not to be limited to BOF nor to chemically bonded brick. In such furnaces (BOF) temperatures can be as high as 3100.degree. F. (1700.degree. C.). It is important that the atmosphere inside the furnace lining, i.e., within the brick comprising the lining, be reducing and, therefore, the invention is not designed for use for and in, for example, open hearth furnaces. This is because the carbon in the improved brick of this invention would not readily prevent oxidation of the metal elements in an open hearth furnace (there would be too much oxygen present) but it does prevent oxidation of such elements in a basic oxygen furnace wherein there is an absence of any substantial source of oxygen within the brick comprising the furnace lining. More specifically, therefore, the invention is directly associated with the making of steel. Those furnaces, or portions thereof, which are shielded to an external metal shell at the cold face may utilize the improved brick of this invention.
2. Description of the Prior Art
A state-of-the-art patent search concerning this invention developed the following U.S. Pat. Nos. 122,908-Perry, 1,672,524-Groninger, 2,216,813-Goldschmidt, 2,652,793-Heuer, et al., 2,764,887-D'Ambly, and 2,853,852-Samuel. The following foreign patents were also developed: Nos. 890,893-British, 575,857-Canada and 1,471,111-German. No assertion is made, however, that the foregoing patents represent the closest art although it was indeed the intent of the search to develop such art.
With reference to the patents noted above, the British, Canadian, and Heuer, et al patents all disclose brick having metal ribs or reinforcements. Apparently the primary reason for such reinforcements is to provide an anchor or suspension means for the brick within the furnace and to reduce the incidence of spalling from the hot face. No disclosure is made in these patents, however, as to whether or not improved thermal conductivity could be realized by the use of metal ribs if they were in a reducing (non-oxidizing) environment. Apparently these patentees believed that their ribs would oxidize near the hot face and thus subsequently become a part of the refractory, that is, a monolithic refractory would result. Although the remaining patents teach metal encasement and reinforcement and the like, and are therefore of general interest, they do not teach or suggest the furnace and refractory taught herein.
The Heuer, et al patent does discuss the problems in brick which are associated with hot and cold faces; namely, transverse cracks which lead to pieces spalling from the hot face of the brick. This is representative of that well known fact in this art that the thermal gradient which exists between a hot face and a cold face of a brick will result in a very high stress build-up which can and does result in cracking. Specifically, however, the Heuer, et al teachings are applicable to suspended roof brick to be used in an open hearth furnace. Thus, while Heuer, et al do speak of metal plates embedded in refractory brick, and even of adding sulphite pitch to the refractory material, Heuer, et al also speak of the metallic member being oxidizable, a phenomenon which is carefully eliminated in the instant invention.
The Samuel patent discloses a metal cased refractory brick. This is for the purpose of increasing strength. The strengthening principle of Samuel, however, is the same as that taught by Heuer, et al in that the plates are oxidized to iron oxide which fuses into the refractory to result in a monolithic layer, again, a phenomenon which the instant invention carefully avoids.
Reference is also made to British Pat. No. 1,031,584 which, while not developed by the state-of-the-art search, appears to be pertinent. This patent relates to a magnesia brick intended for lining converters, such as BOF, but to a brick which quite specifically is "free of external plates". The patent summarizes its teachings at lines 54 through 62 of column 2 of page 2 as follows. "It has been found that this object can be accomplished by making the lining from refractory, basic or neutral brick, particularly magnesia bricks, which are free of external plates and characterized by the combination of the features known per se that they contain tar only as a binder rather than in the form of an impregnation and comprise co-moulded internal plates."
Another patent which has come to light is British Pat. No. 1,368,635 which is of interest for its disclosure of a cold-bound carbon-containing basic refractory brick incorporating graphite therein.
Additionally there are other patents known to be relevant to chemically bonded brick, and to direct bonded brick, generally: Representative U.S. patents disclosing chemically bonded brick are Woodhouse, et al. No. 3,475,188; Davis, et al. No. 3,479,194; and Farrington, et al. No. 3,615,776. U.S. patents disclosing direct bonded brick are Wright No. 3,715,223; Farrington, et al. No. 3,829,541; Davis No. 3,852,080; and Farrington, et al. No. 3,864,136.
Reference is also made to the following publications: "Transactions and Journal of the British Ceramic Society", Vol. 71, No. 6, pp. 163-170 September, 1972; "Journal of the American Ceramic Society", Vol. 56, No. 11 November 1973, pp. 611 and 612; "American Ceramic Society Bulletin", Vo. 55, No. 7 July 1976, pp. 649-654; and "Journal of the American Ceramic Society", Vol. 59, No. 11-12, November-December, 1976, pp. 529 and 530. These articles discuss and explain the vaporization of Mg from MgO within, but near the hot face of, the brick to form a dense zone between the carbon-containing part and the hot face of the brick.